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{-# LANGUAGE OverloadedStrings #-}
module Network.Wai.Handler.WebSockets
( websocketsOr
, websocketsApp
, isWebSocketsReq
, getRequestHead
, runWebSockets
) where
import Control.Exception (bracket, tryJust)
import Data.ByteString (ByteString)
import qualified Data.ByteString.Char8 as BC
import qualified Data.ByteString.Lazy as BL
import qualified Data.CaseInsensitive as CI
import Network.HTTP.Types (status500)
import qualified Network.Wai as Wai
import qualified Network.WebSockets as WS
import qualified Network.WebSockets.Connection as WS
import qualified Network.WebSockets.Stream as WS
--------------------------------------------------------------------------------
-- | Returns whether or not the given 'Wai.Request' is a WebSocket request.
isWebSocketsReq :: Wai.Request -> Bool
isWebSocketsReq req =
fmap CI.mk (lookup "upgrade" $ Wai.requestHeaders req) == Just "websocket"
--------------------------------------------------------------------------------
-- | Upgrade a @websockets@ 'WS.ServerApp' to a @wai@ 'Wai.Application'. Uses
-- the given backup 'Wai.Application' to handle 'Wai.Request's that are not
-- WebSocket requests.
--
-- @
-- websocketsOr opts ws_app backup_app = \\req send_response ->
-- __case__ 'websocketsApp' opts ws_app req __of__
-- 'Nothing' -> backup_app req send_response
-- 'Just' res -> send_response res
-- @
--
-- For example, below is an 'Wai.Application' that sends @"Hello, client!"@ to
-- each connected client.
--
-- @
-- app :: 'Wai.Application'
-- app = 'websocketsOr' 'WS.defaultConnectionOptions' wsApp backupApp
-- __where__
-- wsApp :: 'WS.ServerApp'
-- wsApp pending_conn = do
-- conn <- 'WS.acceptRequest' pending_conn
-- 'WS.sendTextData' conn ("Hello, client!" :: 'Data.Text.Text')
--
-- backupApp :: 'Wai.Application'
-- backupApp = 'Wai.respondLBS' 'Network.HTTP.Types.status400' [] "Not a WebSocket request"
-- @
websocketsOr :: WS.ConnectionOptions
-> WS.ServerApp
-> Wai.Application
-> Wai.Application
websocketsOr opts app backup req sendResponse =
case websocketsApp opts app req of
Nothing -> backup req sendResponse
Just res -> sendResponse res
--------------------------------------------------------------------------------
-- | Handle a single @wai@ 'Wai.Request' with the given @websockets@
-- 'WS.ServerApp'. Returns 'Nothing' if the 'Wai.Request' is not a WebSocket
-- request, 'Just' otherwise.
--
-- Usually, 'websocketsOr' is more convenient.
websocketsApp :: WS.ConnectionOptions
-> WS.ServerApp
-> Wai.Request
-> Maybe Wai.Response
websocketsApp opts app req
| isWebSocketsReq req =
Just $ flip Wai.responseRaw backup $ \src sink ->
runWebSockets opts req' app src sink
| otherwise = Nothing
where
req' = getRequestHead req
backup = Wai.responseLBS status500 [("Content-Type", "text/plain")]
"The web application attempted to send a WebSockets response, but WebSockets are not supported by your WAI handler."
--------------------------------------------------------------------------------
getRequestHead :: Wai.Request -> WS.RequestHead
getRequestHead req = WS.RequestHead
(Wai.rawPathInfo req `BC.append` Wai.rawQueryString req)
(Wai.requestHeaders req)
(Wai.isSecure req)
--------------------------------------------------------------------------------
-- | Internal function to run the WebSocket io-streams using the conduit library.
runWebSockets :: WS.ConnectionOptions
-> WS.RequestHead
-> (WS.PendingConnection -> IO a)
-> IO ByteString
-> (ByteString -> IO ())
-> IO a
runWebSockets opts req app src sink = bracket mkStream ensureClose (app . pc)
where
ensureClose = tryJust onConnectionException . WS.close
onConnectionException :: WS.ConnectionException -> Maybe ()
onConnectionException WS.ConnectionClosed = Just ()
onConnectionException _ = Nothing
mkStream =
WS.makeStream
(do
bs <- src
return $ if BC.null bs then Nothing else Just bs)
(\mbBl -> case mbBl of
Nothing -> return ()
Just bl -> mapM_ sink (BL.toChunks bl))
pc stream = WS.PendingConnection
{ WS.pendingOptions = opts
, WS.pendingRequest = req
, WS.pendingOnAccept = \_ -> return ()
, WS.pendingStream = stream
}